import java.util.*;

public class Exercise84{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    String str = sc.next();

    if(n == 1){
      System.out.println("NO");
    }else if(n == 2){
      if(str.equals("01") || str.equals("10")){
        System.out.println("NO");
      }else{
        System.out.println("YES");
      }
    }else if(n == 3){
      if(str.equals("010") || str.equals("101")){
        System.out.println("NO");
      }else{
        System.out.println("YES");
      }
    }else{
      System.out.println("YES");
    }
  }
}